While playing the game, press Start to display the options menu. Then, hold L1 + L2 for ten seconds. Keep those buttons held and press Right(2), Left, Down(2), Up, Triangle, Circle. If you entered the code correctly, the extra option "Health" will appear. Select it to refill the life bar.

Refill ammunition

While playing the game, press Start to display the options menu. Then, hold L1 + L2 for ten seconds. Keep those buttons held and press Down, Right, Circle, Left, Right, Circle. If you entered the code correctly, the extra option "Ammo" will appear. Select it to increase your ammunition up to a 32,000 round limit. However, the game may display problems if 15,000 rounds are exceeded.

Maximum firepower

While playing the game, press Start to display the options menu. Then, hold L1 + L2 for ten seconds. Keep those buttons held and press Down, Right, Down, Right, Triangle. If you entered the code correctly, the extra option "Power" will appear. Select it to set your gun's firepower to maximum.

Enter the "Health refill" code to enable the "Health" option on the options menu. Then, pause the game immediately after dying, and before regenerating. Use the "Health" option to refill the life bar. Your character can now move around as a splattered corpse, totally invulnerable to enemies. However, since your own actions are limited, this trick is of limited value. However, it is an interesting thing to try on level 6 or during a two player game.